1. Field of the Invention
The present invention relates to a cap device that is detachably attached to a tank opening member.
2. Description of the Related Art
One known example of the cap device is disclosed in JP No. 10-329861A. FIG. 38 is a partly broken view illustrating a prior art fuel cap 200 for a vehicle. The fuel cap 200 includes a casing body 202, and a cover 210 attached to an upper flange 204 of the casing body 202. The flange 204 has an outer ring element 206 for fixation of the cover 210 and a linkage element 208 for linkage with the casing body 202. The linkage element 208 has a fragile portion including a notch 209. The fragile portion makes a starting point of breaking the linkage element 208 when a large external force in any of diverse directions is applied to the flange 204 via the cover 210. In the case of application of a large external force onto the periphery of the fuel cap 200, for example, due to a collision of the vehicle, this structure breaks the linkage element 208 at the fragile portion and thereby keeps the sealing properties of a fuel tank from the outside.
The fuel cap 200 of the prior art structure may, however, be broken at the fragile portion to be unusable even by a simple inadvertent use other than a collision of the vehicle, for example, a careless drop of the fuel cap 200 during fuel supply or application of a twisting static load to the lower end of the cover 210.
Setting the breaking load at the fragile portion to a specific range of loading, which excludes the possible load level in the case of the inadvertent use, however, has lots of difficulties, since the setting is adjustable only by the direction and the depth of the notch 209 in the narrow flange 204.